1. Field of the Invention
This invention relates to an electrostatic drive device applicable to a semiconductor exposure device, a precision processing machine, a precision measurement device, etc., and to a circuit for controlling such an electrostatic drive device.
2. Description of the Related Art
As shown in FIG. 8, an example of a conventional drive device applicable to a semiconductor exposure device comprises a fixed portion 2 provided with a permanent magnet 1, and a movable portion 6 resiliently supported on the fixed portion 2 by four coil springs 3 and having an iron core 5 on which a coil 4 is wound. The iron core 5 is arranged to oppose the permanent magnet 1 and is capable of being attracted thereto.
The iron core 5 is attracted to and repelled from the permanent magnet 1 by a magnetic force produced by passing a current through the coil 4, thereby driving, i.e., moving and displacing, the movable portion 6.
However, since the coil 4 in this drive device produces heat, not only is a large amount of power consumed but the movable portion 6 and fixed portion 2 also experience thermal deformation, making it difficult to achieve highly accurate positioning. In addition, since the permanent magnet 1 and iron core 5 on which the coil 4 is wound are required, it is difficult to make the device small in size and light in weight.
In an attempt to solve these problems, a drive device of the kind shown in FIG. 9 has been proposed, in which a piezoelectric element 7 is arranged between the fixed portion 2 and movable portion 6, with the movable portion 6 being driven by deformation of the piezoelectric element 7.
However, owing to hysteresis or creep exhibited by the piezoelectric element 7, the displacement of the element is not constant and the amount of displacement is likely to change. Consequently, it is essential that a displacement sensor be provided and that the output signal of the sensor be fed back to achieve control. The result is a more complicated control system.